<!DOCTYPE HTML>
<style>
body {
  background-color: green;
}

#thediv {
  background-color: green;
  width: 300px;
  height: 100px;
  position: absolute;
  top: 20px;
  left: 20px;
  z-index: 2;
}

#theshadow {
  background-color: black;
  width: 300px;
  height: 100px;
  position: absolute;
  top: 23px;
  left: 23px;
  z-index: 1;
}
</style>

<div id="theshadow">&nbsp;</div><div id="thediv">Foo</div> 
